It looks like there was some confusion here. OpenCL C++ extension (for host side) is released by KHRONOS, and is available at khronos site. But BOLT internally uses static C++ kernel language (for kernel side), that is only supported by AMD. So bolt as of now is only for AMD. Here is Kent Knox's reply for more information

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BOLT library requires static C++ kernel language extension implemented in the runtime to work seamlessly across platforms and these extensions are currently part of AMD OCL runtime only.

BOLT library also has AMP backend support for a subset of the OpenCL enabled routines.

However there is a fallback planned and it will occur if there is no AMD GPU device found. If other GPU devices are found, MultiCoreCPU code path using TBB. If TBB is not enabled or installed then Serial code paths will be supported for the below routines: